To study the role of Tat proteins in innate immune responses of newborns and adults, we run quantitative RT- PCR analysis for various cytokine/chemokine genes in monocytes and DCs derived from cord blood and adult peripheral blood. Purified moncytes and monocyte-derived DCs are exposed to exogenous recombinant Tat B and Tat C. Our data indicate that the exogenous Tat proteins differentially stimulate expression of cytokines and chemokines, such as IL-12p40, IL6, CXCL10, HuMIG and ISG15. To extend these studies we are testing different preparations of Tat B and C proteins in newborn and adult monocytes and DCs. Effect of the different Tat proteins are also examined following toll like receptor and interferon stimulation to document altered gene expression.